Google is expected to reach a market share of almost 30% of the online advertisement market this year. The biggest threat to Google's domination of the online advertisment market does not seem to be competitors like Yahoo! More likely, the communities that pop up every now and then from basically nowhere are the biggest threat to Google. Not one community alone, but all of them together. Why? Well, community members voluntarily give away a lot of detailed information about themselves, their interests and lifestyle, which makes it possible to target specific audiences and present personalized offers to them. They are also more willing to accept this targetet advertising, since it is more relevant to them.
Google, on the other hand, tries to get as much information about their users via their services without the users really giving it to them, or without the users even knowing that Google has access to their information. It seems to be a successful strategy. But still, this is a more cumbersome, expensive and problematic road to travel than the one that communities are travelling. Google is well aware of this. Who really thinks Google bought http://www.youtube.com/ for another reason than to get hold of information about the members? I surely don't. They are not really interested in the content itself.
Hence, it is reasonable to suspect that Google will continue to buy popular communities where the members provide lots of information about themselves. But, can they buy enough communities to retain their current market share on the online advertising market? That is, in a near future where the online advertising market will shift from a strong focus on search engines and public portals to blogs and communities?